This research overview looks at a paper in this month’s Journal of Strength and Conditioning Research that sparked my interest from the title. I found myself wondering what the premise of the research was and why it was chosen by the researchers. The idea was for Inacio et al to gain a greater understanding of the effects of changes in bodyfat on certain performance characteristics and this was achieved by adding an external upper body load in the form of a weighted vest. Another aim of the research was to look at any gender differences in simulated fat mass increase and performance decrement.
It was hypothesized that there would be a significant drop in vertical jump, 40 yard sprint, 20 yard sprint and 20 yard shuttle test performances (it is interesting to see the effect that the NFL combine testing is having on research, or is it the other way round?) when an external load of 2% body weight was added, a significant and progressive drop in performance would be seen when loads of 2, 4, 6, 8 and 10% body weight was added and that female participants would show greater decreases than men in all loading conditions. The reasoning for the final hypothesis was that as a result of greater percentage bodyfat amongst women and effectively increasing that through external loading would lead to a greater fat mass to lean mass ratio than compared to men who would start with a lower bodyfat percentage.
There were 46 participants (21 men and 25 women) in the study that made up one experimental group, all were considered untrained, normally active and none participated in an organised sport or physical activity. Each participant completed vertical jump, 40 yard sprint (20 yard sprint measured at the same time) and 20 yard shuttle tests in random order at 0, 2, 4, 6, 8 and 10% external loads that were achieved with weighted vests. Testing took place over 4 sessions interspersed by at least 48 hours for each participant with the first session being body composition testing (DEXA) and baseline (0%) measures. Subsequent sessions were each focused on one physical test and loading order was randomised to minimise the impact of fatigue.
Given the nature of the study with gender, the 6 test conditions and the 4 tests compared, the results took some interpreting. Significant drops were seen in vertical jump scores with the only gender difference being between a significant drop between the 8-10% scores females that wasn’t seen amongst the males. Women also had a significantly greater drop compared to men for every loading condition compared to baseline except at the 6% condition. A similar trend was seen during the twenty yard shuttle test with women showing a greater performance decrement than men in all but the 4% condition.
During the 20 yard sprint a significant drop was seen between 2-6% in women but not men and between 6-8% in men but not women, a progressive drop was seen through all 5 conditions in both genders. In the 40 yard test, performance decrements began at 2% for both men and women but women were significantly more affected by the external load and as a result experienced greater drops in performance at 4,6,8 and 10%.
The results demonstrate the negative effects that higher fat mass can have on performance in anaerobic events. Putting this in a little bit of perspective helps, a 2% increase in mass for a 70kg person is 1.4kg. It would be interesting in future studies, as mentioned by the authors, to look at more athletic populations to if similar performance decrements exist.
Inacio, M., Dipietro, L., Visek, A.J. & Miller, T.A. (2011) Influence of upper body external loading on anaerobic exercise performance. Journal of Strength and Conditioning Research 25(4) pp. 896-902/